1. Field of the Invention
The present invention relates to a planetary type gear unit with sun, planet and ring gears and a planet carrier, said planet carrier comprising a planet bogie plate and at least one planet shaft, whereby on both sides of the bogie plate a planet wheel is mounted on the planet shaft by means of taper roller bearings.
More specifically but not exclusively the present invention relates to a planetary gear unit of the mentioned type for use in a wind turbine.
2. Description of the Related Art
Such planetary type gear units are known according to the state of the art.
In the technology of wind turbines for example there is a tendency to integrate components in order to reduce the overall weight so that the related loads and resulting stresses on the structure of the wind turbine can be minimized.
Typical integration is obtained by the use of a planetary type gear unit whereby the bearing supporting the planet carrier also serves as a main bearing for supporting the rotor hub to which the planet carrier is connected.
However, a consequence of using one main bearing is that the support of the rotor hub, as well as the planet carrier is less rigid than in the more classical designs whereby the rotor hub is supported by separate bearings.
This causes misalignments between the planet carrier and the ring wheel which vary during the rotation, hereby augmenting the risk of damage to the planet wheels.
A known solution to this problem is the use of a so-called bogie plate on the planet carrier.
Such a bogie plate is provided with planet shafts, whereby on both sides of the bogie plate planet wheels can be mounted on each shaft by means of planet bearings.
It is known that such a planetary gear stage with a bogie plate on the planet carrier allows for some misalignments between the planet carrier and the ring wheel without negatively affecting the gear meshing.
Often taper roller bearings are used for the support of the planet wheels, since these type of bearings are able to bear a considerable load in axial, as well as radial direction.
Nevertheless, the planet bearings are one of the more sensitive parts of the gear unit.
Premature failure of the presently known planet bearings is a common problem, which can be caused by dynamic effects due to the clearance in the bearings and to deformations of the bearings under influence of the load.
Furthermore, the more the designs get integrated, the more the space available between the planet carrier and the planet wheels becomes limited, which complicates for example the assembly and the maintenance of the gear unit or adjustment of certain components.
Another disadvantage of the presently known gear units is that the assembly of the planet bearings, especially of taper roller bearings, requires a considerable axial space, which limits the compactness of the design.
Still another disadvantage of existing gear units is that the proper assembly of the planet bearings is only possible when the planet carrier is dismounted.